1. Field of the Invention
The present invention relates generally to a patient monitoring system and method. More specifically, it relates to such a system and method that exhibit improved reliability and accuracy in electromagnetically noisy environments (e.g., environments in which significant amounts of ambient electromagnetic energy are present) compared to the prior art. Although the present invention finds particular utility in the area of monitoring a patient's cardiac function while the patient is undergoing electro-cautery surgery, other uses are also contemplated for the present invention, including monitoring of other anatomical conditions (e.g., brain electrical activity, respiratory function, etc.) and/or in other electromagnetically noisy environments.
2. Brief Description of Related Prior Art
Many conventional systems exist for monitoring patient anatomical and biological functions. For example, systems exist that can monitor a patient's heart and lung activities. One example of a conventional heart activity monitor is the electrocardiograph (ECG), which utilizes sensors placed on the patient's chest to generate electrical signals indicative of the patient's heart activity. These signals are carried by conductive wires or leads to a high gain electronic amplifier block that amplifies the signals from the sensors. The amplified electrical signals are then carried by additional electrically conductive wires to a remote signal processing system, such as a computer display system and/or other type of device (e.g., a printer) for providing to medical personnel a visual depiction of the monitored heart activity. Digital signal processing equipment may also be provided at the remote processing system to determine whether, and provide warning to medical personnel if, the monitored heart activity exceeds or falls below maximum and minimum safe thresholds, respectively, therefor. Also, in such patient monitoring devices, electrical isolation devices (e.g., a coupling transformer, miniature optocoupler system, etc.) are provided to protect the monitored patients from hazardous electrical shocks from the devices.
Typically, if a patient is undergoing certain types of medical and surgical procedures, it is desirable to monitor simultaneously the patient's heart and/or lung activities. These types of medical procedures include procedures making use of high energy equipment, which can generate magnetic fields and other types of electromagnetic interference. Such interference can induce stray currents in the connection wires and in the amplifier block itself, as a result of relatively large capacitances generated in the conducting wires and across the amplifier's isolation boundary (e.g., provided by the transformer coupling, miniaturized optocoupling, etc. used to provide shock protection to the patient). This injects noise into the signals being transmitted from the amplifier block to the remote processing system by providing a return path to ground via the capacitance between the amplifier block and the remote processing system. This reduces the reliability and accuracy of such monitoring equipment.
For example, in certain types of invasive medical procedures, an electrocautery device is used to carry out tissue cutting and coagulation operations. More specifically, such electrocautery devices may be used to generate high voltage, high frequency (e.g., radio frequency) electrical energy that may be applied to the patient to cut tissue or cauterize blood vessels. For the reasons discussed above, if an ECG is being used to monitor patient cardiac activity when this electrical energy is generated, electrical interference noise can be injected into the signals transmitted from the amplifier block to the remote processing system. This injected noise can distort the signals from the amplifier block to such a degree that they no longer accurately indicate monitored heart activity. As can be readily appreciated, this significantly reduces the accuracy and reliability of such conventional monitoring equipment. Thus, it would be desirable to provide a patient monitoring system that does not suffer from these disadvantages and drawbacks.
It would also be desirable to provide a control system that can be actuated remotely from the patient (e.g., at the remote processing system) to generate signals for controlling operation of the ECG, and that is designed to substantially prevent injection of noise into the control signals from ambient electromagnetic interference. As can be appreciated, unless such noise is substantially prevented from influencing the control signals generated by the control system, the control signals actually supplied to ECG may not accurately indicate the commands that are intended to be provided to the ECG.